Processes of removing fluorine from



Patented Oct. 10, 1944 PROCESSES F REMOVING FLUORINE FRO SUPERPHOSPHATECharles A. Butt, Atlanta, Ga., assignor to International Minerals &Chemical Corporation, New York, N. Y., a corporation of New York NoDrawing. Application July 1, 1941, Serial No. 400,646

6 Claims.

This invention relates to the removal of fluorine from superphosphate,triple superphosphate, or mixtures of the two. The material that isproduced is suitable for animal food.

- The superphosphate referred to is the article of commerce used largelyas a fertilizer, made by treating ground phosphate rock withapproximately and equal weight of 50 B. sulphuric acid. It .is composedfor the mostpart of gypsum, CaSO4, and monocalcium phosphate, CaHdPO-r)2, with small amounts of free phosphoric acid and fluorine compounds.

- The triple superphosphate sometimes referred to. as "treble or doublesuperphosphate is the article of commerce used largely as a fertilizer,madeby treating ground phosphate rock with phosphoric acid, or mixturesof phosphoric and sulphuric acids. It is composed largely of monocalciumphosphate, with smaller amounts of gypsumyfree phosphoric acid, andfluorine compounds.

- In prior attempts to remove fluorine from triple superphosphate byheating the same at elevated temperatures, troubles have arisen becausethe monocalcium phosphate fused and stuck to the or SO: gases'whichproved difficult to condense.

Also, when rotary heaters were used to calcine the triplesuperphosphate, the fusing caused the material to roll up into largeballs which stuck to the sides of the calciner, making the operationdifllcult. Besides, the fused condition of thematerial caused fluorineto be entrapped inside the ba1ls,'thus interfering with its removal.

.In' attempts to remove fluorine from superphosphate which contains alarge amount of calcium sulphate, by'heating the same at elevatedtemperatures, although the material did not fuse or become sticky,serious'difliculties developed due to the copious evolution of S02 andS03 gases.

The followingis an example of difficulties that have been encountered inattempts to remove fluorine from superphosphate:

Triple superphosphate of the following analysis: Moisture 3.22%, totalP205 48.85%, citrate insoluble P205 0.98%, available P205 47.87%, freephosphoric'acid (P205) 3.94%, and fluorine 2.06%, was calcined for 15minutes, with frequent stirring, at 8'75900 C. When the temperature hadreached 300 C. the material began to soften and fuse, and the tendencyto fuse increased as the temperature was increased. It was necessary toremove the material, because of its gummy condition while hot, from thefurnace and allow to cool and become brittle, before it could be brokenup and stirred. After each such treatment the mass would again fuse andstick together when the temperature was further increased. The finalproduct contained 0.026% fluorine, and 65.54% P205. When ground 100%through mesh it showed on analysis a solubility of the P205 in 0.4%hydrochloric acid solution of only 24.32% when 0.2 gram of sample wasstirred in 200 cc. of the acid solution for 6 hours at a temperature of98-99 F.

By the present invention difficulties due to fusing and sticking, orevolution of troublesome sulphur gases, during the heating period areovercome by adding a basic alkaline earth compound, such as high calciumlimestone, dolomite, hydrated lime, or calcium oxide to thesuperphosphates before heating to temperatures sufficient to causefluorine to be removed. More specifical- 1y, by having more than enoughof the basic alkaline earth compound to neutralize the free acidpresent, or having present an excess thereof above the amount requiredto form monocalcium phosphate with the free phosphoric acid, thetendency of the mass to fuse or evolve sulphur gases when the materialis calcined is overcome, while a sufficient amount of fluorine isremoved to make the material suitable for animal food; that is, lessthan about 0.20% of fluorine remains.

For example, in carrying out the present invention, water or phosphoricacid is added to a mixture of superphosphate, or triple superphosphate,or a mixture of the two and lime, and the mixture is stirred while thewater or phosphoric acid is being added. It is then allowed to standuntil the lime is neutralized, then calcined, whereupon the fluorine isreduced to less than about 0.20% without difficulties due to fusing andsticking of the material or evolution of the troublesome sulphur gases.

The following are given as illustrative specific examples of ways tocarry out the invention, but it is understood that the invention is notrestricted to these examples.

Example I 100 parts by weight of triple superphosphate of the sameanalysis as in the example above showing fusing'and sticking, were mixedwith 14 parts of powdered calcium carbonate and 40 parts of water. Themixture was then permitted to stand until it set. It was then dried andcalcined for 20 minutes at 900 C. with frequent stirring. The

material did not become fused or sticky. The resulting product contained0.047% fluorine and 55.00% P205. It was ground 100% through 60 mesh anda portion on analysis showed a solubility of the P205 of 98.80% by thesame method as explained above.

" ramme II The same 3.5 Example I, except that 28 parts of CaCOs and 60parts of water were used. The material did not fuse or become sticky.The' remaining fluorine was 0.129%, and the product was readily solublein 0.4% hydrochloric acid solution. I

Example III 100 parts by weight of triple superphosphate. of the sameanalysis as in the example above Emample IV 1040 partslby weight oftriple ,superphosphate of the-same analysis as in Example III were mixedwith 13.3 parts hydrated lime and ,14

parts of. water. After standing 2 days it was screened through 8 mesh,then calcinedfor minutessat 875-900 C. with frequent stirring.

The material did not become fused or sticky. The final product contained0.024% fluorine, and was readily soluble in 0.4%. hydrochloric acidsolution. I

ErampleV Example VI 100 parts by weight of superphosphate of the sameanalysis as in Example V were mixed with 8.7 parts .of. powdered calciumcarbonate and 33 partsof water andcured for 2 hours. The mass was thencalcined for 15 minutes, with frequent stirring, at a temperature of 8000. Only a I slight amount ofSOz and S03 gases was evolved. The finalproduct contained-0.056% fluorine, and

was readily soluble in dilute hydrochloric acid.

Example VII 0 100 parts by weight ofhsuperphosphate of the same analysisas in Example V were mixed with 5.3 parts of hydrated lime and 4 partswater. The mixture was cured 1 day and then calcined for 15 minutes,with frequent stirring, at atemperature of 875-'900"C. with only slightevolution of S02 and SO; gases. The final product contained 0.034%fluorine and was readily solu ble in dilute hydrochloric acid.

phoric'acid added into monocalcium phosphate phosphate) Example VIII77.8 parts by weight of superphosphate of the same analysis as inExample V and 22.2 parts triple superphosphate of the same analysis asin the example above showing difficulties were mixed with 10 parts ofhydrated lime and 6 parts water and leftto cure for four hours.

appreciable evolution of S02 and S0: gases. The final product contained0.060% fluorine, and its solubility in dilute hydrochloric acid washigh.

Example IX parts by weight of superphosphate of the same analysis as inExample V were mixed with 29.6 parts of powdered CaCOa and 61.8 parts of25 B. commercially pure phosphoric acid (24% P205 solution). The amountof CaCOa added was sufficient theoretically to convert the phos-' with19 parts inexcess. The mixture was ai1-' lowed to set, then broken downand allowed to cure for 4 days. It was then calcined for 1 5 minutes,with frequent stirring, at a temperature of '875-900 C. There was noappreciable evolution of S02 or S03 gases. The final prod uct contained0.033% fluorine, and was readily soluble in' dilute hydrochloric acidsolution.

In the claims, where the expression. basic alkaline earth compound isused, it is intended toinclude dolomite, high calcium limestone orcalcium carbonate, hydrated lime, andcalcium oxide. The wordsuperphosphates is intended to include: superphosphate, superphosphateto which phosphoric is added for the purpose of increasing the P205content, triple superphosphate (sometimes called treble or doublesupertriple superphosphate, or other materials the phosphorus content ofwhich is chiefly in the form of monocalcium phosphate.

What is claimed is:

r 1. The process of removing fluorine from triple superpho'sphates,which comprises adding there'- to an amount of a basic alkaline earthcompound sufficiently in excess of that required to neutralize the freeacid so as to prevent fusing or evolution of sulphur gases duringcalcination and heating to a temperature sufiiciently high to removeenough fluorine to render the product safe for use in animal food.

2. In the process of removing fluorine from triple superphosphate, thestep which com.- .prises adding to the superphosphatean-amount of abasic alkaline earth compound sufllciently in excess of that required toneutralize the free acid so, "as to form monocalcium phosphate with thefree phosphoric acid present and an excess above this amount to preventfusing or evolution of sulphur gases when heatedat a sufficiently hightemperature to remove enough fluorine to render animal food.

3. The process of removing fluorine from triple superphosphates, whichcomprises adding thereto an amount of a basic'alkaline earth compoundsufiiciently in excess of that required to neutralize the free acid soas to prevent fusing or evolution of sulphur gases and heating'to atempera.- ture sufliciently high to reduce-the fluorine in the calcinedproduct to less than 0.20%.

4. .The process of removing fluorine :from. triple:

The. mass was then screened through 8 mesh and .calcined for 15 minutes,with frequent stirring",

at a temperature of 875-900 C. Therewas no mixtures of superphosphateand the product safe for use in superphosphates, which comprises addingthereto an amount of a basic alkaline earth compound sufliciently inexcess of that required to neutralize the free acid so as to preventfusing or evolution of sulphur gases during calcination and heating to atemperature of about 875-900 C. 5. The process of removing fluorine fromtriple.

superphosphates, which comprises adding there to an amount of calciumcarbonate sumciently in excess of that required to neutralize the freeacid so as to prevent fusing or evolution of sulphur gases duringcalcination and heating to a temperature sufflciently high to removeenough fluorine to render the product safe for use in animal food.

6. The process of removing fluorine from triple superphosphates, whichcomprises addin thereto an amount of hydrated lime suiiiciently inexcess of that required to neutralize the free acid so as to preventfusing or evolution of sulphur gases during calcination and heating to atemperature sufliciently high to remove enough fluorine to render theproduct safe for use in animal food.

CHARLES A. BUTT.

